JP3472811B2 - Coloring method for polymer moldings - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coloring method,
In particular, it relates to a method for coloring a polymer molded body using carbon dioxide in a supercritical state.

[0002]

2. Description of the Related Art Conventionally, coloring of polymer moldings has been carried out by injection molding or extrusion molding after mixing a polymer pellet with a pigment and kneading with an extruder or the like. in this way,
It is advantageous in that coloring can be performed simultaneously with molding.
Further, it has been carried out by molding a polymer pellet by extrusion molding or injection molding and then spraying an oil-based paint on the surface of the molded body.

[0003]

However, in the above-mentioned coloring by kneading, there is a problem that it takes time to switch colors when changing the colors. That is, once a certain color is used for coloring, there is a problem that the pigment used remains in the apparatus such as the extruder used for molding and it is impossible to immediately color it with another pigment. Further, in extrusion molding and injection molding, if the molded product is colored with a pigment at the same time as molding, the dispersibility of the pigment tends to be non-uniform. Further, since the pigment is colored even inside the molded product, the amount of the pigment used becomes unnecessarily large, which is uneconomical. In addition, when the polymer body is molded by extrusion molding or the like, it is necessary to melt the polymer body, and it is difficult to color a substance that decomposes at a temperature below the melting point of the polymer body.

On the other hand, in the case of the method of spraying oil paint, it is difficult to uniformly color a complicated molded product having a fine structure.

By the way, recently, it has been found that a substance that is insoluble in gas becomes soluble in supercritical carbon dioxide, and it has been known that anhydrous dyeing of cloth or the like is possible.
In this dyeing, the dyes that can be used are limited to disperse dyes, and the dyeing target is also limited to synthetic fibers such as polyester, acetate, nylon, etc., and natural fibers such as cellulosic fibers and protein fibers, cotton, cloth, etc. On the other hand, there has been little success.

This is because in the case of natural fibers, even if the fibers are swollen by treating them with a certain kind of chemicals and the dyes are pushed into the fibers, the loss of the dyes becomes remarkable by washing.

Further, even in the case of synthetic fiber, the maximum temperature is strictly required within the range in which the physical properties of the fiber do not change. Synthetic fibers are produced by molding them into filaments, drawing them while applying heat, and then heat treating them.
As a result, the orientation of the fiber is increased, and the strength and flexibility of the yarn are obtained. A maximum temperature is required within a range that does not affect the physical properties of the fiber such as strength and suppleness. On the other hand, with synthetic fibers, if the temperature is lowered too much, the dissolution and diffusion of the dye into the fiber is slow due to the nature of the fiber, and dyeing at a low temperature (about 100 ° C. or less) is virtually impossible.

For these reasons, dyeable products have been mainly limited to synthetic fibers and the like. Therefore, it is advantageous from the viewpoint of the economical efficiency of the pigment if it is possible to uniformly color not only the thin fiber and the like but also the molded body. In addition, once a molded product that has been colored can be decolorized, it is advantageous from the viewpoint of recycling. However, there has been no method for coloring economically with few pigments.

Therefore, an object of the present invention is to provide a coloring method which is economical and can uniformly color the pigment.

[0010]

[Means for Solving the Problems] In order to achieve the above object, the inventors have further developed a supercritical extraction technology, and the supercritical carbon dioxide dissolving ability and the impregnation / diffusion of carbon dioxide into a polymer resin. By combining the ability to develop, it came to discover the coloring method of the present invention. The coloring method of the present invention is characterized in that a pigment is brought into contact with a polymer molding having an amorphous layer on at least the surface thereof under a supercritical state of carbon dioxide.

A preferred embodiment of the present invention is characterized in that the temperature of carbon dioxide in the supercritical state is not lower than the glass transition temperature of the polymer bioform and not higher than the melting point.

In a preferred embodiment of the present invention, the polymer molding is selected from the group consisting of polyethylene, polypropylene, polycarbonate, polystyrene, polylactic acid, polyethylene terephthalate (PET), polyvinyl acetate, vinyl chloride and fluororesin. It is characterized by comprising at least one kind of material.

A preferred embodiment of the present invention is characterized in that the polymer molded body contains a plasticizer.

A preferred embodiment of the present invention is characterized in that the plasticizer is at least one selected from the group consisting of methanol, isopropanol and acetone.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the coloring method of the present invention, a pigment is brought into contact with a polymer molding under a supercritical state of carbon dioxide. Here, the supercritical state will be described first. The supercritical state refers to a fluid state in which a liquid does not become liquid even if it is pressurized beyond the critical temperature of a certain substance and does not look like a liquid or a gas. Usually, a state in a region where both temperature and pressure exceed the critical value is called a supercritical state. FIG. 10 shows the relationship between temperature and pressure for the state of carbon dioxide. Carbon dioxide has an inherent critical temperature of 31.1 ° C and a critical pressure of 75.2 kg / square centimeter. The coloring method of the present invention utilizes the fact that even a substance that is insoluble in gaseous carbon dioxide will be soluble in carbon dioxide in the supercritical state.

The use of carbon dioxide in the supercritical state has the following advantages. For example, there is no problem of flammability with respect to other solvents (nonflammable), no harmful presence in the environment, odorless, chemically inert and inexpensive. It is generally considered that the mechanism of incorporating a pigment or other substance capable of dissolving in supercritical carbon dioxide into the resin into the polymer is as follows. Below the Tg of the resin (below the glass transition temperature), since the polymer chains do not move, the adsorption mechanism is predominant, and it seems that the resin will fit into the microvoids existing in the resin. Above Tg, the polymer chains begin to move and the diffusion mechanism becomes dominant, and basically, when the CO ₂ pressure is increased, the amount of CO ₂ dissolved increases, and at the same time, the amount of coloring of the substance dissolved in CO ₂ also increases. It is believed that the rate of coloring depends on the diffusion coefficient of the substance into the polymer. The diffusion coefficient naturally depends on the mobility of the polymer. Mobility increases with increasing temperature. Therefore, temperature is an important operating factor for shortening the coloring time.

Further, in the coloring method of the present invention, there is no particular limitation as long as it is under a supercritical state of carbon dioxide, that is, the pressure is 75.2 kg / cm 2 or more and the temperature is 31.1 ° C. or more. .

The polymer molding to be colored according to the present invention is
At least the surface to be colored has an amorphous layer. It is sufficient that at least the colored surface of the polymer molded body has an amorphous layer, and it is not necessary to have the amorphous layer in all parts such as the inside of the polymer molded body. This utilizes the property that a supercritical carbon dioxide fluid is more likely to diffuse into an amorphous layer than a crystalline one. When the surface of the finished product formed of the polymer molded body is already amorphous, the coloring method of the present invention can be applied as it is. On the other hand, when the surface of the finished product is not an amorphous layer, the amorphous layer can be freely formed during molding such as extrusion molding and injection molding. The method for forming the amorphous layer is a conventional method. For example, when the temperature of the mold is lowered and the mold is rapidly cooled, it becomes difficult to crystallize, and the amorphous layer, that is, the amorphous layer is formed thickly. be able to.

The thickness of the amorphous layer is not particularly limited to the use of the substance to be colored. In addition, the thicker the amorphous layer is, the more the colorant is added, and the deeper the coloring becomes possible.

The temperature of carbon dioxide in the supercritical state is preferably a temperature above the glass transition temperature of the polymer molding and below the melting point. The reason why the temperature is higher than the glass transition point is that if it is lower than the glass transition point, the adsorption mechanism to the microvoids in the resin becomes dominant, and the coloring amount is limited even if the CO2 pressure and the temperature of the coloring substance are raised. The reason why the temperature is equal to or lower than the melting point is that, at a temperature equal to or higher than the melting point of the polymer molded body, the polymer molded body itself melts and the shape of the molded body cannot be maintained. The temperature in the supercritical state is 10 ℃
It is preferable to lower the temperature by 30 ° C. From the viewpoint of preventing deformation of the polymer molded body, and shortening the operation time required for coloring as much as possible, more preferably 15 ° C to 25 ° C from the melting point.
Set to a low temperature.

By appropriately changing the temperature, it is possible to control the thickness of the colored layer for coloring the polymer molded body.

The pressure in the supercritical state can be appropriately changed according to the desired thickness of the colored layer of the polymer molding. Generally, at a constant temperature, the higher the pressure, the more the coloring effect increases. By appropriately changing the pressure, it is possible to control the shade of the color of the polymer molded body.

The polymer molded article to be colored according to the present invention is selected from the group consisting of polyethylene, polypropylene, polycarbonate, polystyrene, polylactic acid, polyethylene terephthalate (PET), polyvinyl acetate, vinyl chloride and fluororesin. At least one material can be used.

Further, the polymer molded body to be colored is
A plasticizer can also be included. The plasticizer has a function of lowering the glass transition point of the polymer molded body. Therefore, a molded product having a high glass transfer can be colored even at a low temperature by incorporating a plasticizer. As a result, the polymer molded body can be colored without raising the temperature, so that extra heat energy is not wasted.

Examples of the plasticizer include organic solvents such as methanol, isopropanol and acetone.
Effectively lowering the glass transition temperature of polymer moldings and supercritical
Acetone is preferable from the viewpoint that the amount of CO _{2 that} elutes is small.

EXAMPLES One example of the present invention will now be described, but the present invention is not construed as being limited to the following example.

Example 1 As a pigment, Disperse Blue ₁₄ (C ₁₆ H ₁₄ N ₂ O ₂ content 95
%) Was used. Polypropylene 1 (melting point 160-170 ° C, Sumitomo Chemical), polypropylene 2 as materials for polymer moldings
(Melting point 150 ℃ -160 ℃, Montel), polyethylene 1 (melting point 1
25-130 ℃, Showa Denko), polyethylene 2 (melting point 125-130
℃, Showa Denko) and polystyrene (glass transition point 100-110
℃, Sumitomo Chemical) was used.

The case of coloring with the apparatus of FIG. 1 will be described below. FIG. 1 shows a batch-type coloring device using an autoclave 1 to which a carbon dioxide cylinder 5 is connected.
A supercritical fluid can be supplied to the autoclave by piping from a carbon dioxide container kept at 30 ° C in the warm bath 6. The pressure in the autoclave can be recorded in the computer by the digital pressure gauge 7. The pressure in the autoclave can be adjusted manually with a valve on the gas purge line. The temperature inside the autoclave can be measured with a thermocouple 2 and recorded in a computer. The temperature inside the autoclave can be adjusted by controlling the temperature of the silicone oil bath 9.

The coloring procedure will be described. First, polymer moldings (polypropylene made by hot pressing /
Put a plate (thickness 8 mm) and a sheet such as polyethylene / polystyrene into the autoclave. The properties of each polymer molding are shown in Table 1 below.

[0029]

[Table 1]

Next, the pigment is placed in a quartz glass container and placed in an autoclave. At that time, it is not necessary to contact with the polymer resin. Further, carbon dioxide is supplied from the cylinder to the autoclave. The inside of the autoclave is brought to a given temperature and a given pressure. The temperature is set to a temperature higher than the glass transition temperature and lower than the melting point of the crystalline polymer resin by about 20 ° C. Hold at a predetermined temperature and a predetermined pressure for a certain time.

After that, the temperature is lowered and then the pressure is reduced to a non-critical state. Then, the colored material is taken out.

The color strength and the depth of the colored layer of the polymer molded article before and after the treatment were observed. In order to make the depth of the colored layer clearer, a rapid pressure reduction operation was performed before lowering the temperature, and the depth of the colored layer inside the molded body was observed by foaming the polymer. The results are shown in Table 2 below.

[0033]

[Table 2]

The coloring results of Experiments 1 and 2 are shown in FIGS. 3 (a) and 3 (b). FIG. 3 shows the coloring situation of polypropylene before coloring and under supercritical conditions. However, the colored body is cut to see the internal state.

FIG. 4 shows the coloring situation of polyethylene before coloring and under supercritical conditions. Polyethylene 1 and polyethylene 2 before coloring are shown in FIGS. 4 (e) and 4 (f), respectively. The coloring results of Experiments 3, 4, 6 and 7 are shown in FIG.
Shown in (b), (c) and (d). The coloring result of Experiment 4 is shown in FIG. 5 (c), which is cut to see the internal state.

The coloring result of Experiment 5 is shown in FIG. 5 (a). Figure 5
(a) shows the coloring situation of foamed colored polystyrene. Only the surface of polystyrene is colored.

As is clear from these results, it can be seen that the polymer molding was favorably colored by the coloring method of the present invention.

Example 2 The same pigment as in Example 1 was used to color polypropylene 1 of Example 1 using the apparatus shown in FIG.

The coloring method will be described with reference to the apparatus shown in FIG. FIG. 2 is a diagram showing a coloring device that can be switched between a distribution type and a batch type.

First, using a siphon type carbon dioxide cylinder 5, carbon dioxide is pressurized in a liquid state by a piston type pump 13. Pressurized liquid carbon dioxide 14
Is gasified to form a carbon dioxide fluid in a supercritical state. Carbon dioxide in a supercritical state is passed through the chamber 15 containing the pigment to dissolve the pigment in the supercritical carbon dioxide fluid. The temperature inside the autoclave 1 is brought to a predetermined temperature. In practice, the temperature was set higher than the glass transition temperature of the polymer molding and lower than the melting point of the crystalline polymer resin by about 20 ° C. A supercritical carbon dioxide fluid containing a pigment is supplied into the autoclave in which the polymer molded body is installed.

After holding for a certain period of time, the pressure is reduced. This causes the surface of the material to be pigmented. The pressure inside the autoclave can be recorded in a computer with a digital pressure gauge. The temperature inside the autoclave is controlled by a micro heater. The results are shown in Table 3.

[0042]

[Table 3]

FIG. 5 (b) shows a coloring photograph of Experiment 8. Figure 5
Shows the foamed colored state of polypropylene 1. From this coloring photograph, it can be seen that polypropylene is colored to the inside.

[0044]

[Comparative Example] Using the apparatus shown in Fig. 1, various kinds of commercially available polymer moldings were tested by applying the coloring method of the present invention. As the commercially available polymer molded product, one containing a plasticizer such as methanol, isopropanol, or acetone was selected.

As target products, plastic model (registered trademark), soy sauce bottle, and polypropylene 1 were used. The results are shown in Table 4. Plastic models 1 and 2 are polystyrene plastic models (available from Bandai). The soy sauce bowl is made of polyethylene.

[0046]

[Table 4]

The results are shown in FIGS. FIG. 6 shows the experiment 9
It is a figure which shows the coloring state of. The head of the plastic model 1 is colored from red to blue. Since the plastic model contains a plasticizer, it has a low glass transition point and can be colored even at low temperatures.

FIG. 7 is a diagram showing a colored state of Experiment 10. The legs of the plastic model 2 are colored from white to light blue. After all, it can be colored at a low temperature, but due to the low heat resistance of the plastic model, it was slightly deformed.

FIG. 8 is a diagram showing a colored state of Experiment 11. Only the body of the soy sauce container is colored. The heat-resistant temperature of the soy sauce container is 85 ° C.

FIG. 9 is a diagram showing a colored state of Experiment 12. Even a molded product made of the same material can be colored by appropriately setting the holding time, pressure and temperature.

[0051]

EFFECT OF THE INVENTION According to the coloring method of the present invention, a polymer molded body can be colored with a small amount of pigment, and there is no waste of pigment, which is advantageous in economic terms.

Further, according to the coloring method of the present invention, since supercritical carbon dioxide permeates into the inside of a complex product,
Even a complicated product can be colored uniformly, which is an advantageous effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a batch-type coloring device using an autoclave to which a carbon dioxide cylinder is connected.

FIG. 2 is a diagram showing a flow-type / batch-type switchable coloring device.

FIG. 3 is a diagram showing a coloring state of polypropylene before coloring and under a supercritical state.

FIG. 4 is a diagram showing coloring states of polyethylene before coloring and in a supercritical state.

FIG. 5 (a) is a view showing a coloring state of foamed colored polystyrene. FIG. 5 (b) is a diagram showing a colored state in which the polypropylene 1 is foamed. FIG. 5C shows a cut cross section of the coloring material of Experiment 4 in order to see the internal state.

FIG. 6 is a diagram showing a colored state of Experiment 9.

FIG. 7 is a diagram showing a colored state of Experiment 10.

FIG. 8 is a diagram showing a colored state of Experiment 11.

FIG. 9 is a diagram showing a colored state of Experiment 12.

FIG. 10 is a diagram showing the relationship between temperature and pressure for the state of carbon dioxide.

[Explanation of symbols]

1. Autoclave 2. thermocouple 3. Polymer molding 4. Pigment 5. Gas cylinder 6. Hot bath 7. Pressure gauge 8. valve 9. Hot bath 10. heater 11. mixer 12. air conditioner 13. pump 14. Temperature-controlled room 15. Pigment chamber 16. purge 17. Restrictor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI D06P 5/20 D06P 5/20 A (56) References JP-A-11-255925 (JP, A) JP-A-2001-226884 (JP , A) Special table 11-507704 (JP, A) Special table 8-506612 (JP, A) International publication 98/007054 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) C08J 7/00-7/18 D06P 1/00-5/00

Claims (3)

(57) [Claims] 1. A supercritical state of carbon dioxide, the polymer molded article having an amorphous layer at least on the surface, the
At a temperature 10 to 30 ° C. lower than the melting point of the polymer molded body,
A method for coloring a polymer molding, which comprises contacting a pigment dissolved in carbon dioxide under a supercritical state . 2. The temperature of carbon dioxide in the supercritical state is not less than the glass transition temperature of the polymer molded body and 15 from the melting point.
The method of claim 1, wherein the temperature is -25 ° C lower . 3. The polymer molding is made of at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polystyrene, polylactic acid, polyethylene terephthalate (PET), polyvinyl acetate, vinyl chloride and fluororesin. The method according to any one of claims 1 and 2, which comprises: